Stacks with exhaust vents AND a condensate drip ring. Plus the kettle is domed. If you leave the flat lid on even partially, you'll notice that the underside is covered in steam condensation. That's the stuff that you don't want to fall back into your wort.

Just gotta ask...have you had a problem from boiling with a partially covered kettle? Because I haven't.

So Rolling Rocks flavor was caused by faulty exhaust which allowed some condensation back into the boil..Does that mean any condensation that drips back in causes DMS? If I use a Hop Spider won't some condensation likely drip back in? Will this cause DMS?

Stacks with exhaust vents AND a condensate drip ring. Plus the kettle is domed. If you leave the flat lid on even partially, you'll notice that the underside is covered in steam condensation. That's the stuff that you don't want to fall back into your wort.

Just gotta ask...have you had a problem from boiling with a partially covered kettle? Because I haven't.

I have had DMS issues before from inadequate boil-off when using Pilsner malt. This was caused by a few different things, from burner problems to an extremely high humidity environment combined with bad ventilation. I'm sure that leaving the lid on partially can be okay in many cases, but it's something that I think you do need to be careful about because it really can cause a problem in the real world (unlike HSA )

So Rolling Rocks flavor was caused by faulty exhaust which allowed some condensation back into the boil..Does that mean any condensation that drips back in causes DMS? If I use a Hop Spider won't some condensation likely drip back in? Will this cause DMS?

Just trying to learn! so don't beat me up for any silly questions.

Well, if some drips back in, it should be able to boil off again. It's more about getting the proper amount of ventilation... not enough and too much DMS precursor will remain, like Ron said.

Once the SMM boils out it doesn't matter if the condensation drips back in.

In theory, that's correct from what I've read. If you boiled for 60-90 minutes uncovered and then put the lid on and continued to boil, there would be little/no SMM left and hence no DMS in your beer.

Now, if you have condensate with SMM dripping back in throughout the boil, you're only removing a percentage of it and it's going to take longer for it to be reduced/removed via boil-off. How long in practice probably depends on a lot of factors.

Once the SMM boils out it doesn't matter if the condensation drips back in.

In theory, that's correct from what I've read. If you boiled for 60-90 minutes uncovered and then put the lid on and continued to boil, there would be little/no SMM left and hence no DMS in your beer.

Now, if you have condensate with SMM dripping back in throughout the boil, you're only removing a percentage of it and it's going to take longer for it to be reduced/removed via boil-off. How long in practice probably depends on a lot of factors.

So what makes both sides of this argument seem a bit dubious to me is that there are assumptions being made regarding the behavior of SMM in its vapor state. Once boiling, the SMM and water vapor are separate - the SMM is no longer dissolved in the water because they are both in a gaseous state. When the water condenses on the lid it doesn't contain any SMM immediately. The SMM would then need to redissolve in the condensate, or condense out itself before redissolving. The rate at which that happens will be determined by things like boiling point, hydrophilicity, etc of SMM.

I'm not sure the research has been done already, but I would imagine you would need to test for varying factors (length of boil, boiloff rate, atmospheric humidity and temp, surface area and shape of lid, yada yada), then run the condensate through HPLC to determine the amount of SMM over time. Or you can just brew some beer and use your palate.

I'm not sure the research has been done already, but I would imagine you would need to test for varying factors (length of boil, boiloff rate, atmospheric humidity and temp, surface area and shape of lid, yada yada), then run the condensate through HPLC to determine the amount of SMM over time. Or you can just brew some beer and use your palate.

Yep, that's what I did after reading about partial covering being OK. I don't know about you guys, but I usually don't measure my beer...I drink it!